1. Field of the Invention
The present invention relates to an ultrasonic endoscope to be used for body cavity examination of upper digestive organs, bronchial tube, and so on.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed in order to observe the interior of an object to be inspected and make diagnoses. Among them, especially, ultrasonic imaging for acquiring interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time and provides no exposure to radiation unlike other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide range of departments including not only the fetal diagnosis in the obstetrics, but also gynecology, circulatory system, digestive system, and so on.
The ultrasonic imaging is an image generation technology utilizing the nature of ultrasonic waves that the waves are reflected at a boundary between regions having different acoustic impedances (e.g., a boundary between structures) Typically, an ultrasonic diagnostic apparatus using ultrasonic imaging is provided with a body surface ultrasonic probe to be used in contact with the object or intracavity ultrasonic probe to be used by being inserted into a body cavity of the object. Further, in recent years, an ultrasonic endoscope in combination of an endoscope for optically observing the interior of the object and an ultrasonic probe for intracavity has been used.
Ultrasonic beams are transmitted toward the object such as a human body and ultrasonic echoes generated in the object are received by using the ultrasonic endoscope, and thereby, ultrasonic image information is acquired. On the basis of the ultrasonic image information, ultrasonic images of structures (e.g., internal organs, diseased tissues, or the like) existing within the object are displayed on a display unit of an ultrasonic endoscopic apparatus main body connected to the ultrasonic endoscope.
As an ultrasonic transducer for transmitting and receiving ultrasonic waves, a vibrator (piezoelectric vibrator) having electrodes formed on both sides of a material that expresses a piezoelectric property (a piezoelectric material) is generally used. When a voltage is applied to the electrodes of the vibrator, the piezoelectric material expands and contracts due to the piezoelectric effect and generates ultrasonic waves. Accordingly, plural vibrators are one-dimensionally or two-dimensionally arranged and the vibrators are sequentially driven, and thereby, an ultrasonic beam to be transmitted in a desired direction can be formed. Further, the vibrators expand and contract by receiving propagating ultrasonic waves and generate electric signals. These electric signals are used as reception signals of the ultrasonic waves.
When ultrasonic waves are transmitted, drive signals having great energy are supplied to the ultrasonic transducers. In this regard, not the entire energy of the drive signals is converted into acoustic energy but a significant proportion of the energy becomes heat, and there has been a problem that the temperature rises in use of the ultrasonic endoscope. However, the insertion part of the ultrasonic endoscope is used in direct contact with the living body such as a human body, and a request that the surface temperature of the insertion part of the ultrasonic endoscope is controlled to a predetermined temperature or less has been made for safety reasons of low-temperature burn and so on.
As a related technology, Japanese Patent Application Publication JP-A-9-140706 discloses a technology of collecting heat generated from a heat source within a probe by using heat collecting means and guiding the heat collected by the heat collecting means to a location apart from the heat source by using heat transfer means such as a heat pipe. However, the outer diameter of the ultrasonic probe needs to be smaller when the ultrasonic probe is inserted into a human body, while the diameter of the heat transfer means needs to be larger for sufficiently high heat transfer coefficient of the heat transfer means. Accordingly, it is difficult to apply the technology of JP-A-9-140706 to an ultrasonic endoscope to be inserted into a human body.
Japanese Patent Application Publication JP-P2006-204552A discloses a technology of cooling a vibrator part by transferring the heat generated in the vibrator part and a circuit board to a shield case via a heat conducting part, and allowing a heat absorbing part including a refrigerant feeder and a refrigerant pipe to absorb the heat transferred to the shield case. However, when the ultrasonic probe is inserted into a human body, the outer diameter of the ultrasonic probe needs to be smaller, and it is difficult to apply the technology of JP-P2006-204552A to an ultrasonic endoscope to be inserted into a human body.
Japanese Registered Utility Model JP-Z-3061292 discloses that a heat transfer structure is provided in contact with an integrated circuit within an ultrasonic transducer, for extracting heat generated there to the outside, and the heat extracted by the heat transfer structure is transferred to an electrically conducting material that functions as a heat sink within a communication cable. However, in an ultrasonic endoscope, the signal cable has a small sectional area, and, in the case where the signal cable is used for heat dissipation, no sufficient heat dissipation effect is obtained due to the small sectional area.
Japanese Patent Application Publication JP-A-63-242246 discloses an ultrasonic probe having a force-feed cooling member mounted on the leading end of a head case. In the ultrasonic probe, a cooling pipe is provided in the force-feed cooling member, and an ultrasonic transducer part is cooled by a cooling medium (e.g., water) flowing through the cooling pipe. However, the outer diameter of the ultrasonic probe becomes larger when the cooling pipe is provided.
As described above, in the conventional ultrasonic probe structures, the outer diameter of the ultrasonic probe becomes larger when attempting to reduce the temperature rise of the ultrasonic probe. Accordingly, development of a new heat dissipation structure is desired in an ultrasonic endoscope.